JP3343803B2 - Zinc alloy powder for alkaline battery and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc alloy powder used as a negative electrode active material for an alkaline battery and a method for producing the same.

[0002]

2. Description of the Related Art A zinc alloy powder for an alkaline battery used as a negative electrode of an alkaline battery in which an electrolytic solution is an alkaline solution such as caustic potash or caustic soda is made of industrial zinc such as electric zinc or distilled zinc. It is manufactured by spraying a molten alloy alloyed with a small amount of additive metal by an atomizing method. Many technical improvements have been made in the past on zinc alloy powder, and mercury-free non-melted powder is now used.

[0003] There are the following cited examples of improved techniques.
For example, Fe, as an unavoidable impurity in the raw material zinc, or a trace amount of impurities mixed from tools and equipment used in the manufacturing process,
There are Ni, Co and other impurities. These batteries promote the corrosion of zinc in a battery and increase gas generation, and as a countermeasure, JP-A-59-33757 states that impurities that cause gas generation are ferromagnetic substances such as iron, nickel, and cobalt. Since these are the substances which are most likely to be mixed, a method of manufacturing a battery having excellent liquid leakage resistance by performing magnetic separation in a strong magnetic field having a magnetic flux density of 15,000 gauss or more is disclosed. Japanese Patent Application Laid-Open No. 61-61365 discloses that "in general, a local battery is formed when two or more metals come into contact with each other, and when they come into contact with an aqueous solution, water is decomposed to generate gas. Nickel and the like generate a large amount of gas when they come in contact with zinc powder in an alkaline liquid, and iron and nickel are not converted into mercury. And discloses an improved technology using lead as the current collector.

Japanese Patent Application Laid-Open No. 61-116755 discloses zinc powder (impurity content when the raw material is electric zinc is Fe:
5-20 ppm, Cd: 1-5 ppm, Cu: 1-10 ppm
, Ni: 1 to 5 ppm, Co: 0.1 to 1 ppm, Ag:
When the raw material is distilled (normal pressure distilled) zinc, the impurity content of the zinc powder is Fe: 100 to 300 ppm, C
d: 50 to 1000 ppm, Cu: 10 to 100 ppm, N
i: 1 to 30 ppm, Co: 1 to 10 ppm, Ag: 1 to 1
0 ppm etc.) alone as the cathode active material,
Even when the battery is not loaded, the zinc powder releases hydrogen in the electrolyte and dissolves in the electrolyte solution, a so-called self-discharge phenomenon occurs, which significantly reduces the life of the battery, so that iron, cadmium, copper, The battery characteristics are improved by specifying the total content of nickel, cobalt and silver as 9 ppm or less.

Japanese Unexamined Patent Publication (Kokai) No. 3-56637 discloses that "impurities contained in zinc promote the corrosion of zinc, and when the purity of zinc is less than 99.995%, particularly when the impurities are Ni and C
When each of r, Mo, Sn, and Sb exceeds 1 ppm by weight, or when Fe exceeds 10 ppm, the amount of hydrogen gas generated increases to such an extent that the effect cannot be ignored and also causes variation. " Each is 1pp
m and 10 ppm or less of Fe and 99.99
An improved technique for improving corrosion resistance by including a specific additive alloy component such as Ga in high purity zinc of 5 or more is disclosed. Japanese Patent Application Laid-Open No. 3-152870 discloses that "usually, zinc is contained in raw material zinc of an alkaline battery zinc alloy in an amount of 1 to 3 ppm. Does not have any effect, and it is considered that this metal powder occupies most of 1-3 ppm, and iron oxide is present in the remaining ppb order. " Melts the zinc
A technique is disclosed in which a molten zinc alloy to which an alloy element is added is filtered through a heat-resistant filter to remove iron oxide mixed in zinc.

Further, JP-A-5-166507 discloses a zinc alloy powder for an alkaline battery having an iron content of 1 ppm or less as an incidental impurity in zinc and containing a specific additive element to improve the leakage resistance of the battery. Is disclosed.

That is, the technology for improving zinc alloy powder for batteries is to minimize and limit the use of specific impurities, which are unavoidable accompanying the production of zinc used as a raw material, and to use equipment used in the production process. The purpose is to prevent trace impurities from being mixed in from instruments and equipment, and to remove accompanying or mixed impurities in the process.

There are a number of techniques for improving battery characteristics by using added alloy components. In recent years, Hg, Pb, Cd, and the like have tended to be reduced due to environmental problems, but the effects of adding other metals have been studied for various metal types. . For example, Al, I
The battery characteristics have been improved by using n, Bi, Ca, Mg, Sb and the like, and selecting the optimum combination by experimentally confirming the appropriate values of the component amounts.

Regarding the improvement of the battery characteristics by improving the properties and physical characteristics including the powder shape, particle size distribution, surface condition, etc., for example, Japanese Patent Application Laid-Open No. 4-284359 discloses a technique in which the bulk specific gravity is specified. Japanese Patent Application Laid-Open No. H5-299087 discloses an improved technique that specifies the true specific gravity.

[0010]

However, in the prior art, it is not enough to regulate the specific impurity content or to specify the added metal. In particular, it is necessary to use one having extremely high zinc purity. In addition, taking measures to prevent or remove impurities from being mixed in the process may lead to an increase in troublesome processes and equipment, an increase in the number of defective products, and an increase in manufacturing costs.

In other words, by reducing specific impurities, the battery characteristics are improved, but the cost is increased. In addition, there are countless combinations of the alloying elements to be added and the optimum combination of the amounts of the alloying elements. No satisfactory zinc powder has been made.

Accordingly, an object of the present invention is to provide a zinc alloy powder for an alkaline battery which greatly suppresses the generation of hydrogen gas due to self-discharge which affects the battery life without using a zinc alloy powder in which accompanying specific impurities are particularly reduced. And a method for manufacturing the same.

[0013]

In the past, efforts have been made to reduce the content of iron as an impurity to the utmost, and this has become technically possible. However, since various problems have occurred as described above, the present invention As a result of intensive studies on means for reducing the influence of iron, the inventors selected a predetermined amount of Al, In, and Bi, and when alloying with this component, Al was first, then dissolved in order of In or Bi. As a result, the present inventors have found that the effect of iron is reduced when the battery is used, and arrived at the present invention.

That is, when the alloy components are dissolved in this order, the iron content, which is determined as an impurity of the zinc powder, becomes 0.00
When the content is more than 01% by weight and 0.001% by weight or less, when the negative electrode active material of a battery is used, its characteristics are maintained in a good state. The zinc alloy powder for a battery of the present invention is composed of Al, In, and Bi as additional alloy elements in addition to the iron content,
More specifically, Al 0.001 to 0.01% by weight, In 0.0
1 to 0.07% by weight, Bi 0.001 to 0.02% by weight
However, the effect cannot be obtained even if the content is out of the range of these components or contained alone.

In short, the content of iron as an impurity is more than 0.0001% by weight and not more than 0.001% by weight. By adding a specific element to this and specifying the dissolution order of the added alloy element, The object is achieved by these synergistic effects.

Accordingly, the present invention provides a method for producing a zinc alloy powder for an alkaline battery, which is obtained by spraying a molten metal obtained by alloying purified molten zinc with a small amount of an additional metal by an atomizing method and then sieving the zinc alloy powder. In the manufacturing method, at the time of the above alloying, Al is first dissolved, and then In or Bi is dissolved in this order.
-0.01 wt%, In 0.01-0.07 wt% and Bi 0.001-0.02 wt%, and F
The present invention provides a method for producing a zinc alloy powder for an alkaline battery, characterized in that a zinc alloy powder containing more than 0.0001% by weight and less than 0.001% by weight of e is used as a negative electrode active material.

[0017]

As described above, in the present invention, industrially used purified zinc which is usually used can be used as a raw material. That is, the Fe content is not particularly limited, but may be 0.001% by weight or less. Dissolve such zinc, then Al,
An alloy component of In and Bi is added to form a zinc alloy.

Al has an effect of smoothing the surface of the alloy powder particles by alloying with zinc, and has an effect of reducing a surface area related to reactivity and suppressing gas generation. I
n has the effect of increasing the hydrogen overvoltage on the surface of the alloy powder to suppress gas generation due to corrosion during storage as a battery, and Bi has the effect of suppressing gas generation before discharge, but increases gas generation after discharge. Tend to.

In the above alloying, Al is used first,
It is necessary to dissolve in the order of In or Bi. If the order of dissolution is changed and Al is left behind, the battery characteristics using Al will deteriorate.

The reason is that when Al is added to and dissolved in zinc, A
Because l is easily oxidized, it also acts as a deoxidizer,
Light dross, which is partially oxidized and forms itself, floats on the dissolved zinc. When alloying by adding Al for the first time, a small amount of iron or iron oxide dissolved in zinc or mixed in zinc partially floats with dross, but is mostly dissolved in zinc.

This mechanism is presumed to be due to the fact that a small amount of iron is dissolved as it is, a small amount of iron is dissolved as it is, and a small amount of iron oxide is partially reduced to metallic iron and dissolved in zinc. Is not clear. Then I
n or Bi is added. Bi and In do not dissolve in zinc and act as oxidizing or reducing agents,
Either one may be dissolved first.

By obtaining a zinc alloy melt to which these alloy elements are added and then performing normal atomization, a zinc alloy powder can be obtained.

[0023]

Embodiments 1 to 18 FIG. 1 is a side sectional view of a gas generation amount measuring apparatus used in an embodiment and a comparative example for obtaining a gas generation speed before electric discharge, which will be described below with reference to FIG.

The purity is usually 99.995% or more, and the content of Fe as an impurity is 0.0001 to 0.001%.
Was melted at about 500 ° C., and a predetermined amount of each element shown in Table 1 was added thereto in a predetermined order to prepare a molten zinc alloy. Next, a high pressure gas was injected by a normal atomizing method to prepare a zinc alloy powder, which was sieved to obtain a zinc alloy powder. About the obtained zinc alloy powder, F
e content and gas generation rate were determined.

Here, the gas generation rate was measured by the measuring device shown in FIG. That is, a predetermined amount of zinc alloy powder 1 is charged, a 40% KOH solution 2 saturated with zinc oxide is added, and then a test tube 5 filled with liquid paraffin 3 and sealed with a silicone rubber stopper 4 is placed in a thermostat bath 60 ° C. Hold on to
The gas generation rate was determined by reading on the scale of the pipette 7.

As shown in Table 1, the iron content is about 0.0001% to 0.001% and has a specific composition, and Al is added first to form a zinc alloy powder. In all of Examples 1 to 18, the gas generation amount is smaller than the allowable limit of about 30 μl / g · day.

[0027]

Comparative Examples 1 to 18 In Comparative Examples 1 to 3, in which only the iron content was changed without adding any alloying component, the gas generation amount exceeded the allowable limit. Comparative Examples 4 to 12 are those in which Al, Bi, and In are added alone or two components selected from them are added, but the content of Fe is 0.0001% to 0.001%, and Even if was added first, the amount of generated gas was above the allowable limit.

In Comparative Examples 13 and 14, the additive component B
Although i is out of the range, even when the Fe content and the order of addition are within a predetermined range or order, the gas generation amount exceeds the allowable limit, and Comparative Examples 15 to 17 show the order of addition of the added components. In each case, the amount of gas generated exceeds the allowable limit. In Comparative Example 18, the Fe content exceeded 10 ppm, and the gas generation amount reached a value that reached an allowable limit.

[0029]

[Table 1]

[0030]

As described above, according to the method of the present invention, the content of iron, which is a typical impurity of zinc powder, is reduced to ppm.
Without special reduction to the order, the specific range (0.0001 to 0.001% by weight), and further contain specific additive alloy components Al, In, and Bi, and the melting order of these alloy components is specified. As a result, the zinc powder for an alkaline battery which can suppress the generation of hydrogen gas and improve the battery characteristics can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a gas generation amount measuring apparatus used in Examples and Comparative Examples to determine a gas generation rate before discharge.

[Explanation of symbols]

 Reference Signs List 1 zinc alloy powder 2 40% KOH solution 3 liquid paraffin 4 silicone rubber stopper 5 test tube 6 constant temperature bath 7 pipette

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-299082 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/42

Claims (1)

(57) [Claims] A molten metal obtained by alloying purified molten zinc with a small amount of additional metal is atomized by atomization to obtain powder.
In the method for producing a zinc alloy powder for an alkaline battery which is sieved to obtain a zinc alloy powder, in the above alloying, Al is first dissolved, and then In or Bi is dissolved in this order. ~ 0.01% by weight, I
n 0.01-0.07% by weight and Bi 0.001-
0.02 % by weight and 0.0001% by weight of Fe
A method for producing a zinc alloy powder for an alkaline battery, comprising using a zinc alloy powder containing more than 0.001% by weight as the negative electrode active material.